This invention relates to a reverse rotation preventing mechanism for synchronous motors wherein the direction of rotation of the synchronous motor is regulated.
Synchronous motors and particularly, those of the inductor type have a characteristic that a shaft rotates in either direction in accordance with the polarity of input power source waveforms at the starting Accordingly, when such a synchronous motor is employed as a drive source so that a load is driven through, for example, a reduction gear mechanism, a reverse rotation preventing mechanism is usually provided for rotating the synchronous motor in a predetermined direction.
FIGS. 8 and 9 illustrate the major part of a conventional reverse rotation preventing mechanism for synchronous motors. A reduction gear mechanism of which only a first-stage gear 1 is shown is provided for driving a load. The first-stage gear 1 of the reduction gear mechanism is formed from a sintered alloy integrally with a flywheel 2. The flywheel 2 has two mounting projections 2a formed on the underside thereof An engagement member 3 comprises a leaf spring formed from phosphor bronze. The engagement member 3 has two ends and is formed into a generally annular configuration. The engagement member 3 is inclined downwardly as it goes from a base end 3a to the other end engaging portion 3b The base end 3a has two mounting openings 3c formed therein. The mounting projections 3c are inserted in the mounting openings 3c, respectively and subsequently, the engagement member 3 is mounted on the flywheel 2 by caulking the mounting projections 2a.
The gear 1 is secured to a rotor shaft of a synchronous motor (not shown). When the rotor is rotated at the starting in the direction opposite to the normal direction, the engaging portion 3b of the engagement member 3 is elastically engaged with a stopping portion (not shown) mounted on a frame of the synchronous motor. Consequently, an elastic reaction force causes the rotor to rotate in the normal direction.
However, since the engagement member 3 is mounted on the flywheel 2 by way of caulking in the above-described conventional construction, the engagement member 3 tends to be deformed during assembling resulting in failure in engagement of the stopping portion with the engaging portion 3b of the engagement member 3 or insufficient engagement therebetween. Consequently, the reverse rotation preventing mechanism does not function properly.
Furthermore, when the load driven through the reduction gear mechanism is relatively light for the synchronous motor, each gear of the reduction gear mechanism is usually formed of a synthetic resin. However, in the above-described conventional construction, the first-stage gear 1 is formed from a sintered alloy and the second-stage gear engaging the first-stage gear is formed of the synthetic resin and consequently, the second-stage gear is apt to wear, thus entailing the problem of durability of the gear.